feat(echo)!: support Echo v5 as module github.com/rennf93/echo-guard/v2

[rennf93]

Closes #51

master moves to Echo v5 as module github.com/rennf93/echo-guard/v2. Echo v4 users stay on v1.x. Branch v1 is at v1.5.0 plus CI bumps (5070976).

Forced signature changes. Every other exported identifier is unchanged.

1. New(engine, opts...) returns Echo v5's echo.MiddlewareFunc.
2. GuardWebSocket(engine, c) takes *echo.Context.
3. NewStatusHandler(engine) returns Echo v5's echo.HandlerFunc.
4. AddStatusRoute(app, engine, path) takes Echo v5's *echo.Echo.

Behavior notes:

• v5 removed c.Error, so a handler error goes through c.Echo().HTTPErrorHandler before the status is read, the same order v1.5.0 used.
• The adapter reaches the *echo.Response with echo.UnwrapResponse (echo v5.4.0 response.go:121) and swaps the capture and held writers underneath it.
• A writer chain that never reaches an *echo.Response, or a handler error on a context without an Echo instance, fails closed with the 500 Security check failed response. Two new tests cover these paths.
• The engine floor is guard-core-go v4.4.1, which stops printing the spec DEBUG lines on every request.

Verified locally:

• On Go 1.26.0: gofmt -l . prints nothing, and go vet ./... and staticcheck ./... pass.
• REDIS_HOST=127.0.0.1 go test -tags integration -coverprofile=cover.out . gives ok ... coverage: 100.0% of statements, and check_coverage.sh gives coverage 100%.
• Both examples build.
• make lint exits 0.
• govulncheck ./... on Go 1.27.2: No vulnerabilities found.